1. The Field of the Invention
The present invention concerns a method and apparatus to monitor the addition of chemicals to a fluid system by determining flow/no-flow condition, controlling fluid flow, and controlling the condition and operation of chemical sensors and, in particular, to a method and apparatus for controlling the chemical balance in swimming pools and the like.
2. The Prior Art
The automatic control of the feeding of chemicals to, for example, swimming pools or industrial baths, requires accurate measuring of the chemical conditions within the pool or bath in order to inject the proper amount of the corrective chemicals. Chemical balances in a flowing liquid system can become inaccurate (out-of-tolerance) and are generally difficult to diagnose when problems arise. The problems can be generally classified in two classes, namely problems in measuring and problems in adding correcting chemicals. The most common measuring problems include: the sensors are dirty; the fluid flow rate past the sensors is too low or too high; the sensors are in contact with air rather than liquid; corrective chemicals that were fed downstream of the sensors are interfering with the sensor readings; and fluid turbulence around the sensors. The most common problems related to the process of adding chemicals into a fluid system are: the injectors may have become clogged thereby limiting the flow of corrective chemicals through the injector; the chemicals don't flow when the device feeding chemicals to the injector is activated; and the addition of chemicals when there is no fluid flow in the system. There is a possible safety problem associated with feeding chemicals in a no-flow condition in that the adjusting chemicals may come in contact with each other in their undiluted condition and cause an unwanted chemical reaction. In order to prevent such a problem from arising, a flow sensing device should be included in the system.
Preferably a control device should have a fail safe way to determine the flow/no-flow condition within the flow cell circuit. A conventional pressure switch located anywhere in the circuit will not provide a satisfactory indication of flow conditions since it will be defeated by a valve being accidentally closed or blocked by debris (a common occurrence). In this condition the system could have pressure but no-flow. Many known flow switches are subject to malfunction due to clogging from foreign matter and they are not subject to visual inspection while in operation. Flow switches must be installed in a proper location in the system to provide protection against accidental chemical injection.
Diagnosing chemical injecting problems is generally a time consuming process and, in many cases, causes the operator to needlessly come into contact with the chemical additives, often in their full strength condition. An operator will typically start by disconnecting one or more of the chemical injectors and, since they are filled with full strength or diluted chemicals, will often get these chemicals on him. Incorrect reassembly may lead to leaking.
The prior art partially addresses some of the problems associated with the sensors. For example U.S. Pat. No. 4,550,011 discloses a device that holds two sensors under a transparent cover which allows one to see if the sensors are dirty. This patent teaches injecting acid directly into the flow cell for cleaning only, not for water balancing, and fails to inject the sanitizer directly into the flow cell. However, this patent doesn't address the problems associated with the chemical injectors, limiting and adjusting the flow rate through the device, providing protection from feeding in a no-flow situation, ease of installation or even limiting the number of components required for installation in a bypass line.
The present invention concerns a method and apparatus that solves all the above listed problems and has additional features of making it substantially impossible for air to become trapped at the sensor tips, provides protection against adding chemicals in a no-flow situation, and substantially reduces or eliminates injector clogging.